ABSTRACT
The term biogeochemical cycle refers to the set of pathways involving biological, geological, and chemical processes, by which a chemical element or substance moves through different environmental matrices (as discussed in Chapter 11). Common synonyms of biogeochemical cycle are turnover or cycling of substances (e.g., P or N cycling). Cycling means that, after a specific amount of time, the substance is found back in the starting phase and the set of pathways is then repeated. For example, circulation of chemical elements, such as carbon, oxygen, nitrogen, phosphorus, calcium, and water, through various ecospheres is referred to as biogeochemical cycle. Depending on the particular environmental conditions, various elements show characteristic cycling periods. While cycling throughout the ecospheres, an element may be accumulated in specific places, called reservoirs. For example, in aquatic ecosystems, phosphorus is often accumulated in the bottom sediment. Generally, reservoirs hold substances for times significantly longer than the cycling period. The length of time that a chemical is detained in one place is called its residence time. When chemicals are seized for a short period, they belong to exchange pools (e.g., plants and animals). Cycling time and storage time are critical factors defining the behavior and role of a particular substance or element throughout its biogeochemical cycle.
